The present invention relates to ceramic materials and methods of production thereof, and more specifically, to ceramic (i.e., inorganic, silicate-based) materials of potentially low density and good thermal insulating qualities.
A number of alkali metal silicate-based insulation materials have been described in the prior art. Characteristic examples of such materials are evident from U.S. Pat. Nos. 4,297,252 (Caesar et al); 4,521,333 (Graham et al); 4,118,325 (Becker et al); and Great Britain Pat. No. 1,227,482. These patents describe well-known methods of hardening an aqueous alkali metal silicate composition to form a gel or solid product. The basic hardening techniques include chemical methods such as adding sodium or potassium fluorosilicate and/or organic gelling agents such as haloalcohols, amines, ketones, etc., or by heating the gel at low temperature (approx. 100.degree. C.) to reduce water content.
Though apparently well-suited to a number of applications, these techniques have a number of serious draw-backs. First of all, methods which involve heating to form the gel are expensive in terms of time and energy consumption. Furhermore, this gel can not be easily molded or extruded. Intumesced ceramics produced from these gels have very little structural strength because of their extremely low density, unless large amounts of filler materials have been incorporated into the starting silicate solution. Gels produced using organic hardening agents are easier to machine because of their plastic-like consistency. However, gels containing organic materials such as haloalcohols and amines present fire and toxicity hazards when heated to produce solidification or intumescence.
Fluorosilicates are usually used in combination with organic hardening agents. When used alone, in sufficient quantity to cause solidification of the silicate solution, the resulting material does not exhibit intumescence (expansion and cell formation) when subjected to temperatures which normally cause this reaction to occur (around 1000.degree. F.) in gels produced by other means. Furthermore, when heated to high temperatures, the fluorosilicate may decompose to produce extremely toxic gasses such as silicon tetrafluoride and fluorine.
It is a principle object of this invention to provide a simple, inexpensive technique for producing alkali metal silicate gels which offer a number of benefits over prior methods.
A further object is to provide a method of producing alkali metal silicate gels which are non-toxic and can be easily molded and machined.
Another object is to provide a method of producing silicate gels which can be heated (to cause intumescence) to produce a variety of low and high density insulation materials.
Other objects will in part be obvious and will in part appear hereinafter.